Nonlinear mode competition and coherence in low gain FEL oscillators

Summary Form only given, as follows. A simple, one-dimensional, multimode model for a low-gain FEL oscillator is being used to study numerically the effect of mode competition on the coherency of the radiation. For a beam current smaller than four times the minimum start-oscillation current, many single mode states are possible. However, the time required to reach these states becomes very long for FEL devices described by a small slippage parameter. Two different time scales characterize the process of reaching a single mode state. The shorter time scale is related to an establishment of a relative constant amplitude of the radiation field while the phase of the field is modulated. The relaxation of the phase takes a much longer time. This process can be described analytically by a model that allows for investigation of the effects of noise and mode locking as the relaxation process.<>